The County Planning Commission on Tuesday approved a plan to relocate or destroy hundreds of trees--some more than 300 years old--to make way for new homes just north of Lake Forest. The plan, prepared for the Foothill Ranch planned community, set a benchmark for future development, Commissioner C. Douglas Leavenworth said. Commissioners said they may refer to it again as housing developments continue to creep into the forested foothills. "This is a precedent," Leavenworth said.

One educational afternoon at the Orange County Planning Commission makes sadly clear why mindless overdevelopment has virtually ruined the former life style of Orange County. I sat as an uninvolved observer while a developer presented his case to build densely on a Santiago Canyon plot of land, then while local residents presented objections. After hearing that the builder intended to remove 1 million cubic feet of sand and gravel from this rural, scenic area, necessitating a trip by a large gravel truck on narrow Santiago Canyon Road every 2 1/2 minutes of every working day for over two years, I was sure that no sane person would approve such an idea.

Orange County Planning Commissioner C. Douglas Leavenworth has wriggled free of the district attorney's conflict-of-interest investigation, a probe best described as some kind of joke. Leavenworth was allowed to simply amend a state-required disclosure form, which reduced the estimated value of gifts he received in 1987 from the Mision Viejo Co., a prominent Orange County development firm, to within a few dollars of state limits. That was all Assistant Dist. Atty. John D.

The credibility of Orange County's planning process has moved up a notch now that Supervisor Don R. Roth has asked for, and received, the resignation of Planning Commissioner C. Douglas Leavenworth. It may be too much to hope that commissioners will henceforth always keep their distance from the people whose proposals they are supposed to evaluate.

Amid complaints that no one knew its potential impact, the Orange County Planning Commission Tuesday demanded further study of a proposal to free some developers of their obligation to provide the county with local parkland.

It should be clear by now that Orange County Planning Commissioner C. Douglas Leavenworth either doesn't understand his role as a trustee for the public or he is very cynical and arrogant about it. Supervisor Don R. Roth, who appointed him, was right to tell him to clean up his act. But from what Leavenworth has done so far, Roth should not be optimistic about a change of heart, and he should at least begin thinking about replacement possibilities.

We're glad the Orange County Planning Commission didn't rush into approving a proposal last Tuesday that would free home builders from requirements to provide local parkland as part of new housing developments. The fact that the potential impact of such a change in park policy still has not been determined was reason enough for delay. But there are even other reasons that make a good case for denial.

C. Douglas Leavenworth, who resigned from the county's Planning Commission in February amid conflict-of-interest allegations, was one of 10 people the City Council appointed to its new Budget Advisory Commission on Tuesday. Also approved were L. Kenneth Heuler, who was ousted by the council from the Public Utility Board in 1987, and Lynne Pierson Doti, a Chapman University economics professor and wife of university President James L. Doti.

The county Planning Commission on Tuesday upheld an earlier recommendation against building a two-lane road in Trabuco Canyon that critics have warned would open hundreds of acres of rugged backcountry to intense development and traffic.

The public is getting a clear glimpse in 1990 of an overall pattern to the way planning has worked at the county-government level in Orange County. It's a portrait of a system awash in money and political influence. This has been especially apparent in the last few years, a period of rapid growth that indelibly has shaped the character of life in the county for years to come.